Development and validation of an online tool to assess perceived portion size norms of discretionary foods

Background: Perceived portion size norms may have shifted toward larger sizes due to widespread exposure to large servings, yet validated tools to assess such norms for energy-dense, nutrient-poor discretionary foods are lacking. Objective: To develop and validate an online image-series tool to examine perceived portion size norms of discretionary foods. Methods: An online tool presenting eight successive portion size options (six for bottled/canned drinks) for 15 commonly consumed discretionary foods was developed. In a randomized crossover laboratory study, adults (18–65 years) reported their perceived portion size norms for each food twice: once using computer-based images and once using equivalent weighed real food options presented at food stations. Agreement between methods was assessed using cross-classification and intra-class correlation coefficients (ICC). Results: Among 114 participants (mean age 24.8 years), >90% of selections were matched in the same or adjacent portion size option. The overall ICC across all foods was 0.85, indicating good agreement. Conclusion: The online image-series tool showed good agreement with real food portion size options and may be valuable for assessing perceived portion size norms of discretionary foods in future research.